According to WebMD, the normal range for CA 125 should be below 35 units per milliliter. However, the normal values can sometimes slightly vary from one laboratory to another. WebMD explains that CA 125 is a biomarker for tumor.
"CA" is a shorhand for cancer antigen, and CA 125 refers to a type of protein which is found in higher concentration in tumor cells than in the other types of cells in the body.
According to WebMD, the amount of CA 125 is commonly measured by taking a blood sample. Additionally, the levels of this substance can also be determined by obtaining fluid from the abdominal cavity or chest. High levels of CA 125 can indicate health problems such as ovarian cancer.